Once that is installed, you can enable HTTP2.
Note: If you are using HTTP2 with Prefork you must use PHP-FPM or FastCGI, mod_php will not work.
If you are using threads or events everything will be fine. Apache 2 on Debian testing defaults to event.

Now enable the protocol in the site that was generated by certbot, e.g.:

vim /etc/apache2/sites-available/kernel.fail-le-ssl.conf

Add the line “Protocols h2 http/1.1”.

systemctl restart apache2

DONE! Welcome HTTP.

p.s.: great video about the benefits and drawbacks of HTTP2: https://www.youtube.com/watch?v=0yzJAKknE_k